1. Field of the Invention
The present invention relates to an IPv6/IPv4 tunneling method that transfers IPv6 packets by encapsulating the same by means of IPv4 packets in sections not corresponding to the IPv6 when carrying out communications among hosts matched to the IPv6.
2. Description of the Related Art
Operating systems and software that support the IPv6 (Internet Protocol Version 6) have become widespread, and utilization environments thereof have been fulfilled. However, the network still depends on the IPv4 base as the main stream. Therefore, there are many cases where even the hosts matched to the IPv6 are obliged to carry out communications on the basis of the IPv4.
As a tunneling technology ensuring IPv6 introduction in the IPv4-based network, ISATAP (Intra-Site Automatic Tunnel Addressing Protocol) is disclosed in non-patent documents 1 and 2. In the tunneling technology, when hosts matched to the IPv6 carry out communications on the basis of IPv6, the hosts transfer IPv6 packets by encapsulating the same by means of IPv4 packets in sections not corresponding to IPv6.
FIG. 3 is an exemplary view depicting one example of the tunneling technology. When a mobile host for which the home network (HN) is based on the IPv6 network is moved to another network (FN) corresponding to the IPv4 and carries out communications in IPv6 with a corresponding host existing on the HN, the mobile host converts IPv6 packets to IPv4 packets by encapsulating the IPv6 packets by means of an IPv4 header and transmits the same to a relay server. The relay server extracts the IPv6 packets by decapsulating the received IPv4 packets, and transmits the same to a corresponding terminal on the HN.
[Non-patent document 1] F: Templin, et al. “Intra-Site Automatic Tunnel Addressing Protocol (ISATAP),” draft-ietf-ngtrans-isatap-22. Txt. IETF, May 2004
[Non-patent document 2] B. Carpenter, et al, “Connection of IPv6 Domains via IPv4 Clouds,” RFC3056, IETF, February 2001
In the prior art tunnel technology described above, there are the following technical problems.
(1) A mobile host must know the IP address of a relay server in advance.
(2) Where a plurality of relay servers are installed, it is desirable that the nearest relay server or a relay server whose load is light is chosen. However, it is not possible to choose an optimal relay server by the prior art technology.
(3) In order to securely carry out charging management by limiting utilization of relay servers to specified users, it is necessary for the mobile host and relay servers to share key information.